It is proposed that the method of Isotope Dilution Neutron Activation Analysis (IDNAA) be developed specifically for accurate measurement of absolute levels of the stable isotopes 64Zn, 68Zn, 70Zn, 54Fe, 58Fe, 63Cu, and 65Cu in human stools, and be combined with a method based on non-absorbable markers Dy, Sm, or Ir in order to provide an accurate fecal isotope balance method applicable to accurate estimation of mineral absorption for Fe, Cu, and Zn under conditions of relative low availability. The integrated method will be tested in human adults and its capabilities and limitations evaluated.